The present invention relates to gas fueled ovens and particularly to built-in wall ovens having pyrolytic self-cleaning capability.
Built-in wall ovens are generally encased on all sides except for the front. Because of the proximity or contact with adjacent and supporting structures which are often wood, the outer surface temperatures of a built-in wall oven must be strictly limited so as to prevent household damage or even fire. With conventional built-in wall ovens that do not have the self-clean feature, sufficient insulation has been an acceptable solution to limiting external surface temperatures because the temperature of the oven compartment typically does not exceed 500.degree.-550.degree. F. However, during a pyrolytic self-clean cycle, the oven compartment is elevated to temperatures in the range from 900.degree.-1100.degree. F. for several hours. Under these extreme conditions, the use of insulation alone is not generally practical for a wall oven. Because of the very high temperatures, a significant amount of heat would pass through any practical type and thickness of insulation, and, with the confinement of a built-in wall oven, extremely hot and perhaps damaging external surface temperatures could be reached.
Attempts have been made to overcome the above-described problem by encasing built-in wall ovens with a spaced jacket or outer casing that creates an air chamber surrounding the oven compartment. A fan has been used to force air through the chamber so as to remove substantial amounts of heat which pass through the insulation layer. In this way, the temperature of the jacket or casing is limited. With electric built-in wall ovens, this technique has proved successful, and many such self-cleaning electric wall ovens have been manufactured.
With gas self-clean wall ovens, there are additional problems. In U.S. Pat. No. 4,375,213, it was recognized that the forced cooling air in the external air chamber could extinguish a gas pilot if one were used, and further, steps were taken to isolate the primary and secondary combustion air from the cooling air so as to provide favorable burning characteristics. However, if there is a bake and broil burner, isolating the primary and secondary air together could result in combustion products from the bake burner being recirculated through the broil burner back to the bake burner when the broil burner is off.